Silicon materials have been known to be used as a constituent element for semiconductors, solar batteries, secondary batteries, and the like. Hence, studies on silicon materials have been carried out actively.
For example, Patent Application Publication No. 1 sets forth a silicon composite in which silicon oxide is coated with carbon by thermal CVD, and sets forth moreover a lithium-ion secondary battery which is furnished with the silicon composite as a negative-electrode active material.
Moreover, in Patent Application Publication No. 2, the present inventors reported the following: reacting CaSi2 with an acid to synthesize a lamellar silicon compound of which the major component is polysilane from which Ca has been removed; heating the lamellar silicon compound at 300° C. or more to produce a silicon material from which hydrogen has broken away; and a lithium-ion secondary battery which is furnished with the silicon material as an active material.
In addition, in Patent Application Publication No. 3, the present inventors reported the following: reacting CaSi2 with an acid to synthesize a lamellar silicon compound of which the major component is polysilane from which Ca has been removed; heating the lamellar silicon compound at 300° C. or more to produce a silicon material from which hydrogen has broken away; furthermore, producing a carbon/silicon composite in which the silicon material has been coated with carbon; and a lithium-ion secondary battery which is furnished with the composite as an active material.